The present invention is directed to cutting foamed thermoplastic material. It finds particular application as a method of cutting foamed insulation material into insulative sheets.
It has been suggested in U.S. Pat. No. 3,788,175 to Pantell to cut rigid foam blocks into segments by employing hot wires. The hot-wires melt the thermoplastic resin from which the foam is made and thereby allows slices to be cut in the material. This method can be employed advantageously to cut the material into sheets so as to provide insulation boards for building and other purposes.
Once the sheets have been cut, it is often desired to provide interlocking edges to provide for tongue-and-groove or ship-lap joints. A method for performing this task is disclosed in U.S. Pat. No. 3,924,495 to DerMarderosian, which disclose the use of two spaced-apart saw blades that made parallel cuts in the edge of the workpiece. A heated knife removes material from the space between the spaced-apart slits produced by the saw blade to provide a groove. The saw blades are smooth and continuous rather than jagged, so that chunks will not be pulled out of the edge of the workpiece
Whatever the effect of the continuous blades may be, it is thought the this sawing results in a certain level of dust production. In addition, it is necessary in this arrangement to feed each sheet sequentially through the machine and provide means for aligning the edges so that the groove is formed at the right position. Accordingly, it is an object of the present invention to cut grooves in a foamed synthetic resin workpiece with production of only a negligible amount of dust. It is a further object of the present invention to provide a plurality of grooves simultaneously and in such a manner that the grooves thus formed are automatically aligned with the faces of the sheets. A still further object of the present invention is to provide relatively sharp edges on the sheets that are grooved and avoid settling marks in the faces of the sheets.